NCI-Agency/anet#822: Update client side schema for Person
NCI-Agency/anet#822: Update client side schema for Person

Make the default Peron endOfTourDate null instead of en empty string.
This fixes an error when submitting the person form without filling the
endOfTourDate.

NCI-Agency/anet,NCI-Agency/anet,NCI-Agency/anet,NCI-Agency/anet,NCI-Agency/anet